1. Field of the Invention
The present invention relates to a planar light source device and a liquid crystal display mounted therewith as a backlight.
2. Description of the Related Art
FIG. 6 is a disassembled perspective view showing an example of a side light type of a planar light source apparatus used as a backlight of a conventional liquid crystal display apparatus and FIG. 7 is a sectional view of a vicinity of a light source of the planar light source apparatus of FIG. 6. In the drawings, numeral 1 designates a lamp comprising a cold cathode ray tube, numeral 2 designates a lamp reflector provided at a surrounding of the lamp 1 for reflecting light emitted from the lamp 1 and radiating the light in one direction and numeral 3 designates a light guiding plate comprising, for example, acrylic species resin having high transmittance of light, which is mounted with the lamp reflector 2 having the lamp 1 at one side face of a long side thereof. Numeral 4 designates a reflection sheet mounted to a side of a rear face of the light guiding plate 3 (side of light reflecting face). The planar light source apparatus constituted by the above-described members, is arranged by making a side of a light emitting face thereof opposed to a rear face side of a liquid crystal display element.
According to the above-described planar light source apparatus, light emitted from the lamp 1, reflected by the lamp reflector 2 and incident on the light guiding plate 3, is propagated in the light guiding plate 3 while repeating total reflection by a difference between refractive indices of the acrylic species resin constituting the light guiding plate 3 and air, scattered by impinging a print pattern for scattering light formed on the side of the light reflecting face of the light guiding plate 3 and emitted to the side of the light emitting face. At this occasion, the light scattered by the print pattern is scattered also to the side of the light reflecting face and accordingly, with an object of preventing the light from leaking out of the light guiding plate 3, the reflection sheet 4 is mounted to the side of the light reflecting face of the light guiding plate 3. Normally, as shown by FIG. 7, the reflection sheet 4 is inserted to inside of the lamp reflector 2 along with the light guiding plate 3.
However, although light incident on the light guiding plate 3 is ideally propagated while repeating total reflection, actually, by a surface roughness of a side face of a light incident portion of the light guiding plate 3 or light invading from a clearance between the light guiding plate 3 and the lamp reflector 2, there causes abnormal light emittance (bright line) at a vicinity of the lamp 1.
With an object of preventing the abnormal light emittance, as shown by FIG. 8, there has been proposed a method of forming a dot pattern 6 absorbing the abnormal light emittance by screen printing at a vicinity of the lamp 1 of the reflection sheet 4. Further, the dot pattern 6 is formed by using a black or gray coating to absorb the light and is printed by a width of several mm through several cm from an end portion of the reflection sheet 4 on the side of the lamp 1. Further, the dot pattern 6 is generally provided with a gradation in which the more remote from the lamp 1, the smaller the shape of the dot pattern 6 becomes.
Further, according to Japanese Patent Laid-Open No.112214/1998, with an object of reducing abnormal light emittance at a vicinity of the lamp 1, there is disclosed a method of projecting the reflection sheet 4 more than the light guiding plate 3 at inside of the lamp reflector 2.
The conventional planar light source apparatus of the side light type is constituted as described above and there has been proposed the method of projecting the reflection sheet 4 more than the light guiding plate 3 at inside of the lamp reflector 2 as a method for preventing abnormal light emittance at a vicinity of the lamp 1. Although conventionally, an electrode portion of the lamp 1 is arranged on an outer side of the light guiding plate 3 since the electrode portion does not contribute to light emittance, in accordance with a request of narrow frame formation of a liquid crystal display apparatus in recent years, electrode portions of the lamp 1 are arranged at both ends of the light guiding plate 3 and there poses a problem that the electrode portion or a lamp holder for protecting the electrode portion interferes with the reflection sheet 4 projected to inside of the lamp reflector 2.
Further, when the dot pattern 6 for absorbing light is printed at the portion of the reflection sheet 4 projected to inside of the lamp reflector 2, there poses a problem that an efficiency of utilizing light is deteriorated and the brightness is deteriorated since the dot pattern 6 inherently absorbs light incident on the light guiding plate 3.
The invention has been carried out in order to resolve the above-described problem and it is an object thereof to provide a planar light source device capable of preventing abnormal light emittance at a vicinity of a lamp without causing a deterioration in brightness and disadvantage in view of structure. Further, it is an object of the invention to provide a liquid crystal display having high display grade by using the planar light source device.
According to an aspect of invention, there is provided a planar light source device comprising a light guiding plate constituted in a shape of a plate, having a light irradiating face for irradiating light at one main face thereof and having at least one side edge in a linear shape at a peripheral edge thereof, a linear light source arranged along the side edge of the light guiding plate, a lamp reflector arranged along the side edge of the light guiding plate to cover the linear light source for reflecting light emitted from the linear light source to inside of the light guiding plate, lamp holders each arranged at inside of an end portion of the lamp reflector for holding the linear light source, and a reflection sheet provided at other main face of the light guiding plate opposed to the light irradiating face, wherein the reflection sheet includes a projected portion projected from the side edge of the light guiding plate to inside of the lamp reflector and end portions of the projected portion are provided with notch portions and accordingly, the reflection sheet is not be deformed by being brought into contact with the lamp holders.
Further, an amount of the reflection sheet projected from the light guiding plate is shorter than 2 mm.
Further, a portion of the reflection sheet proximate to the linear light source is subjected to color printing for absorbing light without a portion thereof projected from the light guiding plate.
According to another aspect of the invention, there is provided a liquid crystal display including a liquid crystal display element in a shape of a plate for sandwiching a liquid crystal material between two sheets of transparent substrates opposed to each other and a planar light source device arranged with the liquid crystal display element at one face thereof, wherein the planar light source device comprising a light guiding plate constituted in a shape of a plate, having a light irradiating face for irradiating light at one main face thereof and having at least one side edge in a linear shape at a peripheral edge thereof, a linear light source arranged along the side edge of the light guiding plate, a lamp reflector arranged along the side edge of the light guiding plate to cover the linear light source for reflecting light emitted from the linear light source to inside of the light guiding plate, lamp holders each arranged at inside of an end portion of the lamp reflector for holding the linear light source, and a reflection sheet provided at other main face of the light guiding plate opposed to the light irradiating face, wherein the reflection sheet includes a projected portion projected from the side edge of the light guiding plate to inside of the lamp reflector and end portions of the projected portion are provided with notch portions and accordingly, the reflection sheet is not be deformed by being brought into contact with the lamp holders.